This invention relates generally to differential line drivers and more particularly to differential line drivers adapted for use in data networks, such as Asynchronous Transfer Mode (ATM) data networks which require the transmission of high speed digital data over unshielded cable, such as an unshielded twisted pair transmission line.
As is known in the art, many new data networks, such as ATM data networks, require the transmission of high speed digital data over unshielded cable. For example, ATM requires 155 megabit (Mb) per second, two level data to be transported via UTP5 (i.e., category 5, unshielded twisted pair transmission line). Each transceiver in the ATM system typically includes a differential line driver, fed by differential binary data, for driving the unshielded twisted pair transmission line. One transceiver 10 is shown in FIG. 1. Here a differential logic input signal 11 is fed to the IN+, IN- pair of input terminals of a differential pair 12, as shown. The differential pair 12 includes a pair of transistors Q.sub.A, Q.sub.B with base electrodes fed by the differential logic input signal 11. The collector electrodes are coupled to a supply voltage, +V.sub.c, via resistors R, as shown, and to the twisted pair 13. The emitter electrodes are connected to a current source, I, as shown.
One key requirement is the conformance to electromagnetic interference (EMI) standards. Use of the twisted pair 13 significantly reduces EMI emission of the differential signal produced by the transceiver 10. However, switching transients resulting from changes in the input signal 11 may produce EMI which requires additional suppression. Such additional EMI suppression is sometimes provided by transformer/inductor modules, such as transformer module 14 shown in FIG. 1. Here, the transformer module 14 includes inductors L.sub.A, L.sub.B, L.sub.C, and L.sub.D, arranged as shown to provide additional EMI emission suppression. While such transformer/inductor module provides additional EMI suppression, such module is relatively expensive.